The present invention relates to a VIR signal detector for a color television receiver wherein hue and chroma gain settings are automatically obtained by use of a vertical interval reference (VIR) signal received on line 19 of a video signal. More particularly, the invention relates to a VIR signal detector for a color television receiver which identifies the reception of a VIR signal with minimum interference from Gaussian and pulse-type noise. Upon detection of a VIR signal, the color television may be automatically switched from manual to VIR signal controlled color tuning. Also, upon loss of the presence of a VIR signal for a sufficient period of time, the receiver is automtically switched into the manual mode of color tuning.
U.S. copending patent application Ser. No. 663,483, VIR Automtic Hue Control with Preference Capability, filed Mar. 3, 1976 by Charles T. Brown et al and U.S. copending patent application Ser. No. 726,182, Chroma Preference Control for VIR Automatic Operation filed Sept. 24, 1976, by Robert O. Banker et al, both assigned to the assignee of the present application, describe circuits for automatically adjusting the color controls of a television receiver using information contained in a transmitted VIR signal.
In both the Brown et al and Banker et al applications a switch is provided to activate the VIR color controls only when a VIR signal is being received in each consecutive line 19 of a video signal. One method by which this switch might be operated is to simply detect the presence of a signal during line 19. The difficulty with this simple form of VIR signal detection is that Gaussian and pulse-type noise present during line 19 could erroneously trigger activation of the VIR color controls.
It is accordingly an object of the present invention to provide a circuit for detecting the presence of a VIR signal in a received video signal.
Another object of the present invention is to provide a VIR signal detector which discriminates against Gaussian and pulse-type noise.
A further object is to provide a VIR signal detector that differentiates between Gaussian and pulse-type noise and the VIR signal to shift receiver color tuning between manual and automatic modes of operation.